1. FIELD OF THE INVENTION
The present invention relates to catalytic hydrogenation of terminal epoxides. The present invention more particularly relates to an improved process for producing primary alcohols at high conversions and selectivities by catalytic hydrogenation of lower, terminal, epoxides which contain a mono-substituted epoxy ring.
2. DESCRIPTION OF THE PRIOR ART
Lower primary alcohols and diols are useful as solvents, particularly in the coatings industry. Other useful materials are derived from these materials, for example the acetates. These materials are also useful as intermediates for producing plasticizers such as dibutylphthalate.
Known methods for synthesizing primary alcohols are: (1) by way of organo-aluminum compounds, (2) by hydrogenation of methyl esters or fatty acids, and (3) by catalytic hydrogenation of aldehydes produced by the Oxo process.
Hydrogenation of terminal aliphatic epoxides to corresponding primary alcohols is also known and is known to be catalyzed by metals such as nickel, cobalt, iron, and copper. The primary alcohols produced, however, contain by-product secondary alcohols, and catalyst systems capable of high conversion with high selectivity to the primary alcohol product have been sought. Japanese Patent Publication No. 73-31083 discloses the production of primary straight chain aliphatic alcohols from 1,2-epoxy straight chain alkanes having at least 3 carbon atoms by liquid phase hydrogenation in the presence of nickel boride, cobalt boride, iron boride, or copper boride at a temperature of 80.degree.-200.degree. C. and a hydrogenation pressure of 20-300 atmospheres.
Senechal and Cornet, "Hydrogenation and Deuteration of 1,2-Epoxybutane and 2,3-Epoxybutane on Metal Catalysts," Bull. Soc. Chim. France, No. 3, pp. 773-783 (1971) reports a study of vapor phase hydrogenation of 1,2-epoxybutane to butanols over Cu,Ni,Pt,Pd,Rh,Ag, and Au catalysts. Ni and Cu catalysts were found to favor cleavage between oxygen and the substituted carbon of the epoxybutane. Both catalysts, however, exhibited a strong tendency to form saturated hydrocarbons. Saturated hydrocarbons represented 22% and 42% of the reaction products over Ni and Cu, respectively, at 140.degree. C. The results reported in the article also indicate significant epoxide isomerization occurred under the conditions employed. The article further notes that catalytic cleavage of epoxy rings is generally studied with reagents in the liquid phase, although, as noted, the studies reported in this article employed reagents in the gaseous phase.
Chernyshkova, F. A., et al., Neftekhimiya, 14 (20), pp. 188-92 (1974) reports a study of the hydrogenation of 1,2-epoxyhexane over zeolite catalysts. The article notes the problem of hydrocarbon formation during hydrogenation of terminal epoxides to alcohols. Zeolites, both with and without hydrogenating metals (i.e., Ni,Pd,Cu,Mo,Fe), were examined. When 1,2-epoxyhexane was hydrogenated over Ni/zeolite Y, the content of primary alcohol in the total alcohols formed was 96%, although the overall selectivity of the epoxide to the primary alcohol was only about 80%.
German Patent No. 1,139,477 discloses a method for producing primary alcohols which contain virtually no secondary alcohols (but do contain paraffin reduction products) by catalytic hydrogenation of terminal, straight chain epoxides having from 7 to 20 carbon atoms per molecule. Group VIII metals (e.g., Co,Fe,Ni) are generally suggested by the patent to be effective hydrogenation catalysts. The hydrogenation catalysts may be prepared as finely-divided metals deposited on carriers or as finely-divided Raney metals. The best selectivities reported in the patent were obtained by adding small amounts of Th,Mg or alkali metals to the catalyst formulation. The process of the German patent may be operated continuously, either under conditions such that the epoxide reactant is in a gaseous state or under conditions such that the epoxide is in a liquid state. In other words, the physical state of materials present in the reaction zone is indicated to have no particular effect on the results obtained. The examples show that hydrogenation of 1,2-epoxyoctane over CoThMg/kieselguhr yielded 86% primary alcohol (the balance of the product being octane). Raney Ni; Raney Co;Co/C;Co/kieselguhr; and and NiThMg/kieselguhr were less selective for primary alcohols (for the C.sub.7 + epoxy compounds studied) than CoThMg/kieselguhr.
U.S. Pat. No. 3,975,449 discloses a process for producing a primary diol and/or triol from a branched chain epoxide wherein the epoxide is hydrogenated in the presence of a solid catalyst comprising Ni or Co at a temperature of 20.degree.-200.degree. C. and a pressure sufficient to maintain the epoxide feed and the diol/triol products in the liquid phase. Suitable epoxide starting materials are defined by the following structural formula: ##STR1## wherein R is an alkylene diradical of 1 to 5 C atoms and R' is a hydroxy alkyl or an alkyl having from 1 to 5 C atoms. Preferred catalyst are Raney Ni, supported Ni, and Raney Co, with Raney Ni being particularly preferred. Hydrogen pressures in the process are within the range from 100-10,000 psig, preferably from 500-5,000 psig.
The primary object of the present invention is an improved process for the hydrogenation of hydrocarbon compounds containing a terminal epoxy ring, and having from 3 to 6 C atoms/molecule, to produce high yields of primary alcohol products. Other objects will be apparent from the following description of this invention.